1. Field of the Invention
The embodiments discussed herein are related to a pattern measurement apparatus and a pattern measurement method, which are configured to measure a pattern by irradiating a surface of a sample with an electron beam.
2. Description of Related Art
Along with miniaturization of semiconductor devices in recent years, an OPC (Optical Proximity effect Correction) mask formed in consideration of optical proximity effect is used in a photolithography process for semiconductor devices. Such an OPC mask requires high precision, and therefore an actually produced OPC mask undergoes a measurement for checking whether or not the mask exactly has a line width as designed.
Conventionally, a line width of a pattern is found by referring to a secondary electron image of the pattern, defining a rectangular measurement region called a ROI (Region of Interest) in such a way as to intersect the pattern, and then measuring a distance between edges of the pattern in the measurement region. The line width cannot be measured precisely if a corner of the pattern is included in the measurement region. Accordingly, the measurement region is defined to selectively include a straight-line portion of the pattern.
In the meantime, since a pattern of an OPC mask is formed by connecting a plurality of small patterns (blocks) to one another in design data, a stepped portion may be formed at a joint between the small patterns. For this reason, even a portion which appears to be a straight-line portion in the secondary electron image may be formed as a small stepped portion in the design data. As a consequence, it is not always possible to measure a line width precisely in a measurement region defined to include a straight-line portion picked up based only on the secondary electron image.